1. Field of the Invention
The present invention relates to a two-armed transfer robot useful for semi-conductor manufacturing equipment, liquid crystal display processing equipment and the like. More particularly, the present invention relates to a two-armed transfer robot for transferring workpieces between processing chambers under a vacuum
2. Description of the Related Art
In general, transfer robots are used for semi-conductor manufacturing equipment, liquid crystal display processing equipment and the like. The robot has at least one arm mechanism provided with a handling member. An object to be processed or workpiece such as a silicon wafer is placed on the handling member. The arm mechanism is capable of moving horizontally in a straight line as well as rotating in a horizontal plane. A plurality of processing chambers for performing various kinds of processing are arranged around a rotation axis of the robot. With the use of the transfer robot, the workpiece is suitably brought to and taken away from a selected one of the processing chambers.
For improving the efficiency of the transferring operation, use is made of the so-called two-armed transfer robot having two arm mechanisms. Each arm mechanism has a free end provided with a handling member.
A conventional two-armed transfer robot is disclosed in Japanese Patent Application Laid-open No. 7(1995)-142552 for example.
Referring to FIGS. 10-13 of the accompanying drawings, the prior art robot includes a stationary base frame 80, an inner frame 81 arranged to rotate horizontally about an axis O.sub.1 relative to the base frame 80 by a suitable driving device, and a first arm 82 supported rotatably about a first axis P.sub.1 extending in parallel to the axis O.sub.1 of the inner frame 81. The first arm 82 is rotated by a suitable driving device attached to the inner frame 81.
Reference numeral 83 indicates a second arm which is rotatable relative to the first arm 82 about a second axis Q.sub.1 extending in parallel to the first axis P.sub.1, while reference numeral 84A indicates a handling member which is rotatable relative to the arm 83 about a third axis R.sub.1 extending in parallel to the second axis Q.sub.1. Reference numeral 85 indicates a first rotation-transmitting member fixed to the inner frame 81 coaxially with the first axis P.sub.1, while reference numeral 86 indicates a second rotation-transmitting member fixed to the second arm 83 coaxially with the second axis Q.sub.1. Reference numeral 87 indicates a third rotation-transmitting member fixed to the first arm 82 coaxially with the second axis Q.sub.1, while reference numeral 88 indicates a fourth rotation-transmitting member fixed to the handling member 84 coaxially with the third axis R.sub.1.
A first connecting member 89 is provided between the first rotation-transmitting member 85 and the second rotation-transmitting member 86, while a second connecting member 90 is provided between the third rotation-transmitting member 87 and the fourth rotation-transmitting member 88. The distance S between the first and second axes is equal to the distance S between the second and third axes. The radius ratio of the first rotation-transmitting member 85 to the second rotation-transmitting member 86 is 2 to 1. The radius ratio of the fourth rotation-transmitting member 88 to the third rotation-transmitting member 87 is also 2 to 1.
Chain sprockets or pulleys may be used for the first to fourth rotation-transmitting members 85-88. Correspondingly, the first and second connecting members 89, 90 may be chains or timing belts.
The first arm mechanism 91 is made up of the above elements 82-90. A second arm mechanism 92, which is symmetrical to the first arm mechanism with respect to the X--X line, is supported for rotation about the second axis P.sub.2 extending in parallel to the axis O.sub.1.
Thus, the distance between the axis O.sub.1 and the first axis P.sub.1 is equal to that between the axis O.sub.1 and the second axis P.sub.2. The two-armed transfer robot is made up of the above elements 80-92.
The operations of the first and second arm mechanisms 91 and 92 of the transfer robot are symmetrical with respect to the X--X line and substantially the same. Therefore, description will be made to the operation of the first arm mechanism 91 below.
First, suppose that the inner frame 81 is kept stationary to the fixed base frame 80, and that the first, the second and the third axes P.sub.1, Q.sub.1 and R.sub.1 are initially located on a common straight line, as shown in FIG. 12. Starting from this state, the first arm 82 is rotated counterclockwise through an angle .theta. about the first axis P.sub.1.
As the result of the above operation, the first rotation-transmitting member 85 is stationary, while the second axis Q.sub.1 is rotated counterclockwise through the angle .theta. to be brought to the Q.sub.11 position. At this time, the Y.sub.1 -side part of the first connecting member 89 is wound around the first rotation-transmitting member 85, whereas the Y.sub.2 -side part of the first connecting member is unwound from the first rotation-transmitting member 85.
Thus, the first connecting member 89 is shifted in the direction indicated by arrows a.sub.1 and a.sub.2. As a result, the second rotation-transmitting member 86 is rotated clockwise about the second axis Q.sub.1.
As previously mentioned, the radius ratio of the first rotation-transmitting member 85 to the second rotation-transmitting member 86 is 2 to 1. Thus, when the first arm 82 is rotated counterclockwise about the first axis P.sub.1 through the angle .theta., the second rotation-transmitting member 86 is rotated clockwise about the second axis Q.sub.11 through an angle 2.theta..
In the above instance, since the second rotation-transmitting member 86 is fixed to the second arm 83, the second rotation-transmitting member 86 and the second arm 83 are rotated clockwise about the second axis Q.sub.1 through the angle 2.theta..
If the second arm 83 is not moved relative to the first arm 82, the third axis is brought to the R.sub.11, position shown by broken lines when the first arm 82 is rotated counterclockwise about the first axis P.sub.1 through an angle .theta., starting from the initial state where the first, the 'second and the third axes P.sub.1, Q.sub.1, R.sub.1 are positioned on the same line. Actually, however, the second rotation-transmitting member 86 is rotated clockwise about the second axis Q.sub.11 through an angle 2.theta.. Therefore, the third axis R.sub.11 is rotated clockwise about the second axis Q.sub.11 through the angle 2.theta., and brought to the R.sub.12 position.
As a result, when the first arm 82 is rotated counterclockwise about the first axis P.sub.1 through the angle .theta. the third axis R.sub.12 is still located on the straight line extending through the first and the third axis P.sub.1 and R.sub.1.
Further, when the second arm 83 is rotated clockwise about the second axis Q.sub.11 through the angle 2.theta. to be brought to the R.sub.12 position, the Y.sub.2 -side part of the second connecting member 90 is wound around the third rotation-transmitting member 87, whereas the Y.sub.1 -side part of the second connecting member is unwound from the third rotation-transmitting member 87.
As a result, the second connecting member 90 is shifted in the direction b.sub.1 -b.sub.2 as shown in FIG. 12. Thus, the fourth rotation-transmitting member 88 is rotated counterclockwise about the third axis R.sub.12.
When the second arm 83 is rotated clockwise about the second axis Q.sub.11 through an angle 2.theta. as described above, the fourth rotation-transmitting member 88 is rotated counterclockwise about the third axis R.sub.12 through an angle .theta. since the radius ratio of the fourth rotation-transmitting member 88 to the third rotation transmitting member 87 is 2 to 1. As a result, a predetermined point C.sub.0 of the fourth rotation-transmitting member 88 is brought to a point C.sub.1 on the straight line passing through the first and the third axes P.sub.1 and R.sub.12.
As described above, the first arm 82 is rotated counterclockwise about the first axis P.sub.1, and the first arm mechanism 91 is actuated in the X-direction, while the handling member 84 fixed relative to the fourth rotation-transmitting member 88 keeps its initial attitude as being moved along the line passing through the first and the third axes P.sub.1 and R.sub.1.
Likewise, the second arm mechanism 92 is actuated in the X-direction, while keeping its initial attitude along the line passing through the first and the third axes.
The handling members 84A, 84B of the first and the second arm mechanisms 91, 92 are fixed between the axis P.sub.1 and the axis P.sub.2. Further, the extremities of the handling members 84A, 84B are vertically spaced from each other. Thus, when the first and the second arm mechanisms 91, 92 are moved in a straight line, the handling members 84A, 84B are moved along the X--X line passing through the axis O.sub.1 without interfering with each other.
When the inner frame 81 is rotated about the axis O.sub.1, the first and the second arm mechanisms 91, 92 are simultaneously rotated about the axis Q.sub.1.
A suitable number (six for example) of processing chambers 71-76 are arranged around the axis O.sub.1 of the two-armed transfer robot. With such an arrangement, transferring and processing operations for workpieces are performed.
However, according to the prior art teaching, the rotation radius of the inner frame 81 is rather large since the axis P.sub.1 of the first arm mechanism 91 and the axis P.sub.2 of the second arm mechanism 92 are spaced from each other, with the axis O.sub.1 of the inner frame 81 located therebetween.
Therefore, the bearings 93 facilitating the rotation of the inner frame 81 relative to the base frame 80 have an unfavorable large diameter. The magnetic fluid seal 94 used for sealing the rotating portion suffers the same problem. Consequently, the overall size of the robot is increased, and the price of the robot is high due to the use of the large bearings 93 and magnetic fluid seal 94.
Further, the driving devices for linearly moving the handling members 84A, 84B of the first and the second arm mechanisms 91, 92 are mounted on the inner frame 81. Thus, the driving devices are rotated together with the inner frame 81. For supplying thus arranged driving devices with electricity, use is made of a cable extending from the base frame 80. Thus, the rotation angle or the number of rotations of the inner frame 81 is limited to prevent the cable from breaking.
A suitable monitoring device is needed for preventing the inner frame 81 from rotating clockwise or counterclockwise beyond a predetermined critical angle (540.degree. for example). The use of such a monitoring device makes the robot expensive. More importantly, the monitoring device does not serve to facilitate the operation of the robot since the device cannot remove the above limitation on the rotation angle of the inner frame.
Further, there is another problem involved in the arrangement where the first and second arm mechanisms 91, 92 are simultaneously rotated together with the inner frame 81.
Specifically, referring to FIG. 13, the following are assumed. Silicon wafers to be processed are initially stored in the chamber 72. Upon successive actuation of the first and second arm mechanisms 91, 92, two wafers are placed on the first and second handling members 91, 92, respectively. One of the wafers will be transferred to the processing chamber 73 and the other to the chamber 71.
In such an instance, the inner frame 81 mounting the first and second arm mechanisms 91, 92 is rotated through a suitable angle. Then, the wafer carried by the first arm mechanism 91 is shifted to the chamber 73.
Thereafter, the inner frame 81 is rotated so that the second arm mechanism 92 faces the chamber 71. Then, the wafer carried by the second arm mechanism is shifted to the chamber 71.
In the above instance, the chamber 71 has a long waiting time before the operation to the chamber itself is started. Specifically, the waiting time includes a rotation time needed for the inner frame 81 to rotate from the chamber 72 to the chamber 73, a shift time needed for the first arm mechanism 91 to move the wafer into the chamber 73, and an idle rotation time needed for the inner frame 81 to rotate from the chamber 73 to the chamber 72.
As is easily understood, the above waiting time will become longer as the distance between two selected chambers become greater. In addition, the same operation as described above may be repeated with respect to all of the chambers 71-76. Thus, the total waiting time accumulated through the working hours is considerably long.
Under these circumstances, the advent of a two-armed transfer robot exhibiting a shorter waiting time and good productivity has been desired.